This project will examine the familial and genetic basis of developmental phonology disorders, the most prevalent group of communication disorders in children. Behavioral and molecular genetic techniques will be used to differentiate clinically based phenotypes of developmental phonology disorders, including phonology disorders in isolation, phonology disorders that are comorbid with other language disorders, and developmental apraxia of speech. A large cohort of sib pairs, N=500, ascertained through a proband with a phonology disorder, will be examined on measures of phonology, expressive and receptive language, speech, and reading. Data analysis, including segregation analyses, will examine family resemblance, sibling correlations, and heritability. Model-free approaches to genetic linkage analysis based upon sibling pairs will be used to evaluate candidate genes that have been associated with phonological processing abilities in studies of reading. Gender differences in phenotypes and modes of transmission of phonology disorders will be examined. Longitudinal follow-up of individuals with histories of preschool phonology disorders will provide data on adolescent outcomes for speech, language, reading, spelling and writing abilities. The overall aim of the project is to improve understanding of genetic basis, behavioral phenotypes, and developmental outcomes of phonology disorders.